S.D. Codified Laws § 58-16-14
The persons eligible for insurance under § 58-16-12 shall be all of the employees of the employers or all of the members of the unions, or all of any class or classes thereof determined by conditions pertaining to their employment, or to membership in the unions, or to both. The policy may provide that the term "employees" shall include retired employees, and the individual proprietor or partners if an employer is an individual proprietor or a partnership. No director of a corporate employer shall be eligible for insurance under the policy unless such person is otherwise eligible as a bona fide employee of the corporation by performing services other than the usual duties of a director. No individual proprietor or partner shall be eligible for insurance under the policy unless he is actively engaged in and devotes a substantial part of his time to the conduct of the business of the proprietor or partnership. The policy may provide that the term "employees" shall include the trustees or their employees, or both, if their duties are principally connected with such trusteeship.
SDCL 58-16-14